1. Field of the Invention
The present invention relates to an upright vacuum cleaner that controls an input to a power-driven fan by detecting the quantity of dust and dirt (hereinafter the dust and dirt will be referred to as dust) passing through an air path. In general, areas to be vacuumed by a vacuum cleaner include a bare floor, a carpeted floor, stairs, walls and ceilings, and in this specification they will hereinafter be referred to as "floor".
2. Description of the Prior Art
There is known a canister vacuum cleaner that controls an input to the fan, but no upright vacuum cleaner having such a capability is known.
Referring to FIGS. 4 to 6, the known canister vacuum cleaner will be described so as to explain the background of the present invention:
The illustrated vacuum cleaner includes a housing 1 having a built-in fan 2, a hose 3, an extension pipe 4, and a suction head 5 including a motor 6 for rotating a rotary brush 7. The extension pipe 4 is connected to the hose 3 through a coupler 8.
The coupler 8 is provided with a variable resistor 9 for controlling the rotations of the fan 2, and a switch 10 for turning on and off the motor 6. The switch 10 houses a light emitter 11 and a light receptor 12 located opposite to the light emitter 11. The housing 1 houses a phase control circuit 13, and a bilateral thyristor 14 designed to control the phase of a voltage applied to the fan 2 in response to a signal from the phase control circuit 13.
The phase control circuit 13 receives a signal from a dust detecting circuit 15 in response to an input from the light receptor 12. The reference numeral 16 denotes the source of power.
This vacuum cleaner is operated as follows:
When the light receptor 12 detects dust passing through a dust passageway, the dust detecting circuit 15 sends a signal to the phase control circuit 13, and a stepped-up voltage is applied to the fan 2 through the thyristor 14 so as to increase the number of rotations of the fan 2 automatically. After the dust passes through the dust passageway, the rotations are reduced. By operating the variable resistor 9, the number of rotations of the fan 2 can be increased or reduced.
When a carpeted floor is being vacuumed, the rotary brush 7 is rotated by turning on the switch 10 to operate the motor 6.
Under the known system described above, the number of rotations of the fan 2 can be adjusted either by operating the variable resistor 9 or by receiving a signal from the dust detecting circuit 15. Whereas the motor 6 is energized or deenergized by turning on or off the switch 10 that does not change the number of rotations of the motor 6. For example, when the fan 2 rotates at a relatively small number of rotations (i.e. R.P.M.), the motor 6 rotates at a constant velocity, thereby causing the suction head 5 to make a noise irrespective of the relatively silent housing 1. In addition so long as the motor 6 is in operation the rotary brush 7 continues to rotate on the carpet even if the carpet has no dust to be cleaned off. As a result, the rotary brush 7 causes wear to the carpet.
To solve this problem, there has been a proposal for controlling the rotation of the motor 6 and the fan 2 together, but this system becomes mechanically complicated with an increased number of components, thereby resulting in an increased production cost.
A further disadvantage is that the surfaces of the light emitter 11 and the light receptor 12 are stained with the dust passing through the coupler 8, thereby reducing the detecting ability.